[en] The effect of low energy argon plasma treatment on the surfaces of polyethylene terephthalate (PET) was investigated by means of contact angle measurement, X-ray photoelectron spectroscopy (XPS), Vickers’ microhardness indentation and atomic force microscopy (AFM). It was observed that the surface free energy (SFE) changes from 42.1 mJ/m² to 85.1 mJ/m² with the increase of plasma treatment time and the corresponding contact angle changes from 60^o to 15^o. The increase in SFE after plasma treatment is attributed to the functionalization of the polymer surface with hydrophilic groups. The XPS analysis shows the increase in C–O and C=O groups after plasma treatment of the polymer surface. The microhardness of the film increases with the treatment time. This may be attributed to the cross linking effect at the surface. Atomic force microscopy (AFM) reveals that average surface roughness increases from 5.8 nm to 49.7 nm as treatment time increases.